Good hygiene is an essential factor in the food production field. Many resources are invested in cleaning and disinfecting the equipment to improve the shelf-life of the products. In addition, during recent years the attention has been focussed on the risk of contamination of food products with pathogenic bacteria. Accordingly, there is an increasing demand for improvements in the field of good hygiene not only with respect to the cleaning, but also in relation to the suitable design of the machines used for the production.
Since 1 Jan. 1995 the EU has prescribed that the machines for processing food products must be designed to support good hygiene and an efficient cleaning procedure which ensures an optimum food product safety. Accordingly, an obvious demand exists for systematically optimizing the hygienic design of machines for processing food products.
An optimum cleaning of a closed process equipment is obtained by ensuring that the cleaning fluids circulate at a sufficiently high flow rate providing turbulent flow throughout the entire process equipment. Dead areas involving a very low flow rate should therefore be avoided by suitable equipment design.
Despite the above efforts, it can be difficult to completely avoid areas in the process equipment in which small remnants of food products stick to the walls of the equipment or accumulate in small pockets and thereby provide growth conditions for unwanted and often pathogenic micro-organisms. As these micro-organisms grow very quickly in the food products being processed in the process equipment, such small residues can very quickly have a serious effect on both health and costs.
Presently, attempts are made to develop materials on which there will be a reduced tendency to form biofilm. Examples are materials having a reduced adhesion to protein and fat and micro-organisms. However, such a solution is unlikely to prevent food remnants and micro-organisms from accumulating in small pockets and cracks. Accordingly, a demand exists for a material with inherent antimicrobial properties.
U.S. Pat. No. 5,843,186 (Christ) discloses an intraocular plastic lens (IOL) with antibacterial activity based on an iontophoretic effect. At least a portion of the lens is made of an iontophoretic composite material including two components, such as silver and platinum, with different galvanic potentials dispersed in a conducting polymer matrix. The iontophoretic effect is obtained when the lens is implanted in an eye. Here saline body fluids penetrate into the polymer matrix and establish a galvanic element between the two embedded components, which causes the ions of one component to dissolve whereafter the ions can migrate out of the matrix and into the surrounding body fluid, where they exert an antibacterial effect. In order to protect the body against harm, the galvanic elements are per se isolated from direct body contact in the surrounding polymer matrix, strong electric field strengths optionally being generated adjacent said galvanic elements.
Due to the use of this known ocular implantate in contact with the eye the antibacterial effect thereof is adjusted to ensure that the body does not suffer any acute or accumulated harm. It is also important that an accumulation of antibacterial ions is avoided for a short or long period.
However, an antibacterial effect based on the iontophoretic principle as suggested by U.S. Pat. No. 5,843,186 (Christ) and adjusted to be used in an implantate is unlikely to suffice for such antimicrobial or other cytocidal uses where the desired effect must be significantly stronger than hitherto known. In addition, an intensification of the effect to release an increased amount of antimicrobial ions results in an increased amount of ion residues in the solution or in the killed micro-organism cells, which cannot be tolerated in many situations, such as in connection with processing of food products.
U.S. Pat. No. 4,886,505 (Haynes et al.) discloses an apparatus to be inserted in the body, such as a catheter. On the surfaces, this apparatus is coated with a first and a second metal in such a manner that a galvanic effect is provided when the apparatus is brought into contact with an electrolyte, such as a body fluid. It is suggested that the two metals are applied onto the surface of the catheter in form of very thin films of a thickness of approximately 5 to 500 nm, either one metal atop the other metal or in such a manner that portions are covered with one type of metal film while other portions are covered with the second type of metal film, a switch being coupled between said two types with the result that the galvanic effect can be switched on and off according to desire.
In one embodiment, the catheter is coated with two metal films, one over the other, and produces a galvanic effect resulting in relatively significant potential differences per distance, viz. high electric field strengths, in an area inaccessible to micro-organisms, i.e. the area at the contact surface between the two films. Thus the antimicrobial effect is based on metal ions being released in the contact layer despite the fact that they are attracted by the cathode material.
In another embodiment, approximately half the surface of the catheter is covered by one type of metal film while the remaining portion of said surface is covered by the second type of metal film apart from an intermediate non-covered portion where a switch is positioned. Here the galvanic effect is indeed active when in direct contact with the surrounding body fluids, but the relatively significant potential differences per distance, viz. the high electric field strengths, only apply to the interface area between the two metal films, whereas the potential difference per distance and consequently the electric field strength is significantly weaker in portions presenting a large distance to said interface area. According to the publication, the antimicrobial effect is obviously also based on released metal ions.
Accordingly, the principle suggested in U.S. Pat. No. 4,886,505 (Haynes et al.) cannot be used in situations where a strong galvanic effect with high electric field strengths across the entire surface is needed without involving a significant release of metal ions.
Therefore, a demand still exists for materials capable of efficiently inhibiting live cells across the entire surface of the material in such a manner that there are no areas or domains with an insufficient antimicrobial effect where unwanted micro-organisms can survive. Such materials are inter alia needed within the food industry where remaining live micro-organisms in the production equipment, during storage and during transport can cause serious problems such as rapid tainting of the product and disease-causing effects in the consumer. These problems are particularly serious when the processed food products are nutrient mediums for the micro-organisms in question and consequently can promote the growth of said micro-organisms. Such food products are for instance dairy products, meat and fish products, gravy, juice, lemonade, beer, wine or soft drinks.